Prepare the Tin: Line a slice tin with baking paper.
Melt the Chocolate: Melt the chocolate in a glass bowl over a pot of simmering water. (You can also melt it in the microwave in short bursts, stirring in between.)
Combine Ingredients: Once melted, remove the bowl from the heat. Crush the biscuits into small chunks and stir them into the melted chocolate. Add the mini marshmallows and mix everything together until well combined.
Transfer to Tin: Pour the mixture into the lined tin. Use the back of a spoon to spread it out evenly.
Chill & Cut: Refrigerate for 1 hour until set. Remove from the tin and cut into 16 squares.
